Wheelchairs generally include a support frame, a pair of principal wheels mounted on the front part of the frame, a pair of directional wheels, mounted on the rear part of the frame and a small chair mounted on the upper part of the frame. The support frame generally includes a symmetrical structure with respect to the center line axis. Wheelchairs commonly available have proven to be unstable with respect to the common occurrence when an invalid must leave the wheelchair to transfer himself, for example, into an automobile or into any other structure. Normally, the transfer takes place with the invalid first positioning his chair alongside the seat of the automobile into which he is transferring. Next, the invalid must lift himself up from the wheelchair with the strength of his own arms into the automobile seat. This operation is very tiring and hazardous for the invalid. Indeed, it is common that the intervention of a helper is necessary to keep the wheelchair motionless during the transfer procedure and/or to assist the invalid in lifting himself up from the wheelchair.
The above described transfer situation is worse when the invalid is not capable of supporting himself with his arms and/or when the invalid cannot cooperate with the helper to transfer from the seat of the wheelchair to the seat of the car.